NAME OF THE ORGANISM: Ditylenchus dipsaci (DITYDI)

GENERAL INFORMATION ON THE PEST

Name as submitted in the project specification (if different to the preferred name):

Pest category:

Nematoda

1- Identity of the pest/Level of taxonomic listing:

Is the organism clearly a single taxonomic entity and can it be adequately distinguished from other entities of the same rank?

Yes

Is the pest defined at the species level or lower?:

Yes

Can listing of the pest at a taxonomic level higher than species be supported by scientific reasons or can species be identified within the taxonomic rank which are the (main) pests of concern?

Not relevant: Vegetable seed sector

Is it justified that the pest is listed at a taxonomic rank below species level?

Not relevant

Conclusion:

Candidate: Vegetable seed sector

Justification (if necessary):

Remark for ornamentals:
- Allium: There is a large number of Allium species (and within the species, varieties) that are used as ornamentals.
Therefore it is suggested to include all Allium for ornamental use in the present evaluation.
- Ismene (host plant for D. dipsaci as mentioned in Directive 2000/29/EC) is nowadays named Hymenocallis for cultivated ornamental species and varieties.

Data of the presence of this pest on the EU territory are available in EPPO Global Database (https://gd.eppo.int/).

HOST PLANT N°1: Allium cepa (ALLCE) for the Vegetable seed sector.

Origin of the listing:

IIA2AWG

Plants for planting:

Seeds and bulbs intended for planting

3 - Is the pest already listed in a PM4 standard on the concerned host plant?

No

Conclusion:

Evaluation continues

4 - Are the listed plants for planting the main* pathway for the "pest/host/intended use" combination? (*: significant compared to others):

Yes

Conclusion:

Candidate

Justification:

A survey of commercial seeds samples in the UK showed its occurrence in >3% of seed stocks of onions. Seed transmission of D. dipsaci to the planted crop is well established and planting certified nematode-free seeds is recognized as an important control practice for this disease. In Germany, a tolerance level of five nematodes/300 seeds is used to establish the risk of transmission of the pathogen to seedlings. Seed infestation can be controlled by chemical or hot-water seed treatments and by seed health tests to remove infested stocks.
Other sources of infection are nematode-infested soil, infested debris and D. dipsaci-infested weeds. Field control can be by rotation, soil solarization or resistant cultivars, however chemical treatments of soil are not economic for large areas (CABI, 2015).
In conclusion seed is a pathway, and with suitable control measures carried out for the alternative inoculum sources, seed can be considered a significant pathway compared to others.

5 - Economic impact:

Are there documented reports of any economic impact on the host?

Yes

Justification:

D. dipsaci is one of the most devastating plant-parasitic nematodes, especially in temperate regions. Without control, it can cause complete failure of host crops such as onions and garlic. In Italy up to 60% of onion seedlings died before reaching the transplantation stage. Penetration of onion leaves by D. dipsaci causes leaf deformation and leaf swellings or blister-like areas on the surface. The leaves grow in a disorderly fashion, often hang as if wilted and become chlorotic. Young plants can be killed by high infestations. The inner scales of the bulb are usually more severely attacked than the outer scales. As the season advances the bulbs become soft and when cut open show browning of the scales in concentric circles (CABI 2015).

What is the likely economic impact of the pest irrespective of its infestation source in the absence of phytosanitary measures? (= official measures)

Major

Is the economic impact due to the presence of the pest on the named host plant for planting, acceptable to the propagation and end user sectors concerned?

No

Conclusion:

Candidate

Justification:

6 - Are there feasible and effective measures available to prevent the presence of the pest on the plants for planting at an incidence above a certain threshold (including zero) to avoid an unacceptable economic impact as regards the relevant host plants?

Yes

Conclusion:

candidate

Justification:

7- Is the quality of the data sufficient to recommend the pest to be listed as a RNQP?

Yes

Conclusion:

Candidate

Justification:

CONCLUSION ON THE STATUS:

Recommended for listing as an RNQP, based on data (regardless of whether seed or vegetatively propagated).

Seeds:
(a) The crop has been inspected at least once at an appropriate time since the beginning of the last complete cycle of vegetation and no symptoms of Ditylenchus dipsaci have been observed;
or
(b) The harvested seeds have then been found to be free of Ditylenchus dipsaci after laboratory tests on a representative sample;
or
(c) The planting material has been subjected to an appropriate chemical or physical treatment against Ditylenchus dipsaci and the seeds have then been found to be free of this pest after laboratory tests on a representative sample.

EU COM (2016) Recommendation of the Working Group on the Annexes of the Council Directive 2000/29/EC – Section II – Listing of Harmful Organisms as regards the future listing of Ditylenchus dipsaci (Kuhn) Filipvejev;